(a) Field of the Invention
The present invention relates a pulse generator of an ultra-wideband (UWB) system.
(b) Description of the Related Art
In general, an ultra wideband (UWB) system occupies a wider frequency bandwidth than an existing frequency bandwidth. Here, the wider frequency bandwidth means occupying about 20% of the center frequency bandwidth or occupying a frequency bandwidth higher than about 500 MHz. A reason for occupying a wider frequency bandwidth is to communicate without interfering with other narrowband signals by dispersing signal energy to ultra wideband.
In order to have such a wide frequency, a very short pulse is required in a time domain. When such a short pulse is used for communication, a signal can be transmitted with low power consumption due to a low duty cycle, and a transmitted signal is resistant to multipath noise.
As an ultra wideband (UWB) system, a low speed UWB standard system was introduced in IEEE 802.15.4a in 2006. The ultra wideband (UWB) system is generally classified into an impulse radio-UWB (IR-UWB) system using an impulse signal, a chirp spread spectrum (CSS) system using a chirp signal, and a chaotic based UWB system using a chaotic signal like noise.
Particularly, the IR-UWB system has been widely used because there is no limitation in pulse configuration and it has strong correlation characteristic in a distance measurement algorithm such as range. Since the IR-UWB system can be realized with low power consumption, the IP-UWB system can be easily applied to a wireless personal area network (WPAN) or a wireless body area network (WBAN).
Further, it has been a recent trend to exclude a LO/MIXER from a transmitting/receiving unit of an IR-UWB system as a non-coherent system for ultra low power consumption. The LO/MIXER consumes a large amount of power in a transmitting/receiving unit of a communication system. If the LO/MIXER is replaced with a low power consuming unit, a large power gain can be achieved.
In order to replace the LO/MIXER, a method using an all-digital pulse generator has been receiving attention. The all-digital pulse generator is an ultra low power consuming unit because the all-digital pulse generator only consumes power for CV2 that is changed according to capacitance and for sub-threshold leakage. A typical all-digital pulse generator will be described in detail with reference to FIG. 1.
FIG. 1 is a diagram illustrating a typical pulse generator of a UWB system.
As shown in FIG. 1, a typical all-digital pulse generator is a major element in an IR-UWB system excluding a LO/MIXER. Realization of an all-digital pulse generator is directly related to overall system performance and a low cost system. A typical all-digital pulse generator receives pulses modulated through a pulse position modulation (PPM) scheme, and delays the received pulse for a predetermined time using delay cells so as to generate delayed input signals.
The typical all-digital pulse generator outputs a predetermined number of rising/falling edges of the delayed input signals through a mask register having an AND gate, and generates an impulse signal to be used for communication through an edge combiner using an XOR gate tree. The edges having passed through the XOR gates are generated as a fine pulse width having a duty cycle of as much as a delay interval. A center frequency of an impulse signal is determined based on the fine pulse width. The mask register controls a bandwidth of the generated impulse signal by determining the number of fine pulses.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.